Gaseous discharge lighting apparatus



May 11, 1943. E. G. LODGE GAsEous DISCHARGE LIGHTING APPARATUS FiledAug. 3, 1942 llllflIxAllll INVENTOR.

NEKS.

nia-,M0101 444 ATroR Patented May 11, 1943 2,319,144 GAsEoUsmscnaaGELIGHTING mm'rus Edmund G. Lodge, St. Marys, Pa., assigner to StackpoleCarbon Oompany, St. Marys, Ps., a corporation of PennsylvaniaApplication .august 3, 1942, serai No. 453.317

(ci. 11s-124) 8 Claims.

This inventon'relates to electric circuits for gaseous discharge lamps,and more particularly to those in which the lamp is operated from asource of direct current.

A gaseous discharge lamp is one containing a gas that is ionized by apair of electrically heated filaments. An example oi' this type of lampis the tubular fluorescent lamp. One terminal of each nlament isconnected to a sourceof alternating current,'and the other terminals ofthe filaments are electrically connected by a normally closed automaticswitch, such as a bimetallic switch. When the current is turned on,electricity flows through the filaments and switch until the filamentsbecome hot enough to ionize the gas around them. At about the same timethe electrically heated switch snaps open', and the resulting voltagesurge, which may reach 800 or 900 volts or even higher, causesionization of the gas in the tube and reduces the voltage to about 110volts. An electrical device called a ballast is placed in the circuit toprevent the current from burning out the filaments while the switch isclosed.

In many cases it is desirable to use fluorescent lamps and the likewhere there is no priary source of alternating current, such as intrains andr airplanes. It is therefore necessary to make specialprovision for producingv the alternating current necessary to operatethe lamps.l

For this purpose it is common practice to generate alternating currentby means of motor generators or dynamotors driven by the availabledirect current, but they are heavy, bulky, and expensive. Inthe case ofdynamotors their fine and necessarily closely spaced windings often aredestroyed when the load is suddenly removed. That is, to keep down thebulk and weight of dynamotors, the wire size and insulation thickness iskept at a minimum, so any unusual surge of voltage-caused by an opencircuit tends to break through and destroy the insulation. Also,accidental shorts often cause the windings .to be burned open due to thesmall wire size. A multitude of delicate operations are lnecessary tocon neet the armature windings to the commutator segments, causinghazards, and requiring close inspection with resulting high cost. All ofthese disadvantages become particularly objectionable in the case ofairplanes, especially those used in warfare where reliability andreduction in weight are highly important. In warplanes the calibrationsand needles on indicator dials are coated with fluorescent paints andthe lamp tubes are.

left uncoated, resulting in the dials glowing while the black light fromthe lamps is invisible.

Vibrators also are used for the purpose of converting low voltage directcurrent into alternating current so that it can be stepped up by atransformer to a higher voltage. Vibrators have several undesirablefeatures, one of the chief ones being unreliability. The vibration rateof the reed is so limited that fairly large transformers and filters arerequired. As the reed vibrates, the ilow of current removes contactmaterial from one contact and deposits it on the adjoining one. 'I'hisnot only changes the characteristics of the vibrator but it causes thereed to stick. Once sticking begins it is generally necessary to replacethe vibrator. Furthermore, vibrators are relatively expensive for theiroutput because they require very careful adjustments to make themoperable in the nrst place.

- It is among thev objects of this invention to provide gaseousdischarge lighting equipment for battery or other direct currentoperation having means for converting the direct current intoalternating current which is compact and relatively light in weight,which is easy and inexpensive to make, which is self-starting, which ishlighly emcient, and which is sturdy and dependa 1e.

In accordance with this invention the secondary coil of a transformer isconnected to the iilaments of a gaseous discharge lamp, such as a:iluorescent lamp. The primary coil of the transformer has a center tapadapted to be connected to a source of direct current, such as a batteryor direct current generator, that is to be converted into alternatingcurrent for lighting the lamp. By center tap is meant any tap on theprimary coil between its end taps and is not to be understood as meaninga tap at the exact center of the winding. A pair of ilxed electriccontacts are connected to or near the opposite ends of the primary coilfor engagement by rotary contact means adapted when rotating to makeelectrical contact with each of the nxed contacts alternately. I'herotary contact means are adapted to be electrically connected to thesource of direct current to complete the primary circuit. When therotary contact means are driven, the ilow of direct current to each halfof the primary coil is interrupted alternately, and as this currentalternately flows in opposite directions in the primary coil, it inducesalternating current in the secondary coil connected to the lampfilaments. The transformer steps up the voltage of the converted currentto a point where it ls sumcient to operate the lamp.

The means by which the rotary contact means are driven preferablyinclude an amature rotated by electromagnetic means that may consist ofthe transformer itself or a separate electromagnet. In the former. casethe armature is journaled in such a position in the transformer that theleakage flux of the transformer rotates the armature. The primary coilof the transformer, or the electromagnetic coil when a separate coil isused, is connected in the circuit in such a manner that as the rotarycontact means engage rst one fixed contact and then the other, thecircuit through the coil is alternately energized and deenergized toproduce the periodic magnetic impulses that rotate the armature. Thetransformer preferably is purposely made to have poor regulationcharacteristics, such as by winding the secondary with extra fine wire,so that the usual ballast wili be unnecessary. With such a transformerthe load or resistance of the lamp laments before the automatic switchopens brings the alternating current voltage down to one proper forlament operation so that the filaments will not burn out. As soon as theswitch opens and the gas in the lamp is ionized, the voltage increasesto about 110 volts and the'lamp operates.

The preferred embodiment of the invention is illustrated in theaccompanying drawing in which Fig. 1 is a side view of my currentinterrupting device by which direct current is converted intoalternating current for operating a gaseous discharge lamp; Fig. 2 is aview of the opposite side of the device; Fig. 3 is an end view; Fig. dis a plan view; and Fig. 5 is a diagrammatic view of the entire lampcircuit. Y

Referring to Fig. 5 of the drawing, one terminal of each filament i of agaseous discharge lamp 2, such as a'iiuorescent lamp, is electricallyconnected to a normally closed automatic switch 3 which may be athermo-switch having a bimetallic element that opens the switch when itbecomes heated by electric current flowing through it. The otherterminals of the filaments are con-f nected by wires d to the oppositeends of the secondary coil 5 of a transformer 6. The ends of the primarycoil i of the transformer are connected by wires 8 to a pair of xedelectric contacts or brushes S and it that are engaged by a rotatingcontact member li. This contact member includes a pair of diametricallyopposite live contact segments l2 and I3 which are electricallyconnected through a collector button i6 and a wire l5 to a source ofdirect curernt, such as a storage battery I6. The other side of thebattery is connected by a wire Il to the center tap of primary coil 1.It will be seen that as contact member il rotates it connects thebattery with rst one end and then the other of the `primary coil. Thecurrent thus ows alternately in opposite directions through the primaryand thereby induces alternating current in the secondary coil. Thetransformer as a whole steps up the voltage of the alternating currentto a point satisfactory for operation of the lamp.

For an understanding of the details of construction of the device bywhich direct current is converted into alternating current vforoperatingthe lamp, reference should be made to Figs. 1 to 4. As thereshown, the transformer has an E-shape core 20 with a center leg on whichis mounted a coil 2| that is a combination of primary and secondarywindings 1 and 5, respecatraiga tively (Fig. 5). Projecting toward eachother fromthe two end legs of the transformer core are core extensions22 the inner ends of which are spaced apart above the center leg of thecore.

- 'I'he metal laminations forming the core are clamped together at thebottom by bolts Z3 and at the top by bolts 2d.

Mounted on top of core 20 is avcover plate 2S of non-magnetic material,such as brass, which has downturned ears 27 at both ends that overlapthe end legs -of the core. The lower edgeof each ear is notched topermitit to iit over upper bolts 2d and to be clamped by nuts zagainst thecore.

YThe central portion of plate 25 is arched over the gap between coreextensions 22, and this arched portionA projects from both sides of thecore where it forms the upper portions of integral substantiallycylindrical bearing supports 29.

Attached to the outer end of one of the bearing supports is aninsulating plate 3i provided with a pair of outwardly projecting pins 32on each of which one end of a contact arm 33 is pivotally mounted. Thefree ends of these arms carry brushes 9 and lil, preferably made from amixture of powdered silver andy graphite, connected by wires 8 to theends of the primary coil. The two brushes are held by springs (notshown) in engagement with the commutator-like member il mounted on theadjacent end of a horizontal metal shaft 34 journaled in bearings 35mounted in metal bearing supports 29 of cover plate 2S.

The commutator includes the pair of electric contact segments l2 and i3and enough metal segments 35 insulated from them to complete thecylinder without at any time bridging the adjoining brushes. It ispreferred to divide the commutator into six segments of equal sizeembedded in a core 3l of insulating material. The commutator is providedat its inner end with a project ing hub 38 tightly engaging shaft 3d andintegral with the live contact segments but separated from segments 36.Engaging this hub is the smai. collector button It carried at the centerof a flat spring 39 supported at its ends by metal pins di projectingfrom bearing supports 2t. The pins are so positioned relative to theshaft that spring 39 must be bowed slightly so that button is makes goodcontact with hub 38. The contact segments i2 and i3 of the commutatorare thus grounded to cover plate 26 and core 2@ through button tl,spring 39, and pins t l As the battery is ground-= ed to core 20 by wirel5, the contact segments are electrically connected to the battery atall times.

It will thu's be seen that, as the commutator revolves, its livesegments engage first one'brush and then the other. This causes thecurrent from battery I6 to pass alternately through each brush so thatit ows through the primary coil rst in one direction and then the otherto give an alternating current effect. Also, due to the break in thecircuit every time a live segment of the commutator leaves a brush andbefore the other brush is engaged by a live segment, the transformer isalternately energized and deenergized.

The'commutator is rotated by means of an armature 'd5 rigidly mounted onthe central portion of shaft 36. The armature has a plurality of radialprojections or wings, preferably four, spaced at intervals over wheretwo live commutator contacts are used. When either one of the twoprimary contact segments is in engagesions 22. .This leakage iiux ormagnetic impulse attracts the adjacent projection of the amature anddraws it toward it, thereby rotating the armature. This moves the livecontact of the commutator out of engagement with the adjoining brush andbreaks the circuit through the transformer. rotating armature carriesthe other live contact segment into engagement with the other brush sothat the transformer is again energized and another impulse thus givento the armature. In this manner thearmature is rotated at high speed.

Referring more specifically to Fig. 1, the rotor, which consists of thearmature, commutator and supporting shaft. is shown in one of the foursimilar positions it should be in for starting and forrotation in aclockwise direction. The lower right-hand projection of the armature iscloser to the center leg of the transformer core than is any other partof the armature, and contact segment I2 is in contact with upper brushI0 but about to leave it. When the current from battery I6 is turned on,the transformer is energized and the lower right-hand projection of thearmature drawn around toward the center leg of the transformer due tothe effort of the -ux set up in the transformer to close the gap betweenits center leg and the armature or to find the path of least resistance.By the time the armature projection points within about 2 'of straightdown so as to afford a low resistance path for the flux, contact segmentI2 hasleft brush I0 so that the transformer is deenergized, but momentumcontinues the rotation of the armature until contact segment I3 makescontact with brush 9 so that the transformer 'is again energized and thecycle repeated. Shortly after segment I3 leaves brush 8 it moves acrossbrush I0, after which contact I2 engages brush 9, whereby the armatureis continuously rotated at high speed.

In order that the rotor will always be selfstarting, means is providedfor stopping the armature with one of its projections in the positionshown in Figs. 1 and 2 whenever the current to the device is turned oif.For this purpose, as shown in Fig. 2, a hollow cylinder 41, mounted onthe side of the transformer opposite t that from which the commutatormember projects, contains a solenoid coil 48 that is connected in seriesin wire I1 between the battery and a filter condenser Il connected tothat wire and grounded to the transformer core. A fixed core 49 isdisposed in the lower half of the solenoid inside of a tube SII thatprojects above the coil. 'I'his tube guides a vertically reciprocablemovable core I that extends above cylinder 41 and that is urged upwardlyby an encircling spring 52 compressed between the top of the tube andthe bottom of a disc l2 rigidly mounted on the upper portion of themovable core. The upper endY of the movable core is bifurcated andreceives the slotted outer end of an arm 54 the inner end of which ispivoted to the lower portion of a bearing support 29. The arm and coreare pivotally connected by a pin 55. The arm is provided near its innerend with an upwardly extending integral projection 56 from the upper endof which a roller 51 projects outwardly. This roller is adapted toengage the edge of a disc-like cam il rigidly mounted on the projectingend of rotor shaft 3l. The cam is more or less square with a centraldepression in each edge, and it is so `positioned relative to thearmature that when roller 51 engages the cam in any one of its fourdepres- However, the momentum of thesions the armature is in startingposition, which is shown in Figs. 1 and 2.

When the current is turned off, the spring 52 lifts movable core 5I andthereby swings arm il upwardly to press roller 51 against the edge ofthe cam. The rotating cam comes to rest with the roller disposed in oneof its four depressions, and the armature thus is ir. starting position.As

' soon as the current is turned on again the magnetic pull on thearmature is sufcient to cause a high part of the cam to force roller 51outwardly. This action swings the outer end of the arm down and therebyforces the movable core down into the solenoid far enough to bring itinto the eld of magnetic attraction of the fixed core 49. The lattercontinues to draw the movable core downwardly and the roller is thusentirely fleed from the cam so that the rotor is ree to rotate. Lever 54then is in the dotted-line position shown in Fig. 2.

Another feature of this invention is that the transformer is preferablywound to provide poor electrical regulation. This may be done by windingthe secondary coil with extra fine wire. The

regulation is most suitably such that when the current is rst turned onthe voltage of the secondary coil can be held down to about 20 volts bythe electrical resistance of the lamp filaments. With this voltage thereis no danger of burning out the filaments. As soon as the automaticswitch opens there is a surge in voltage up as high as 900 volts orhigher. This causes ionization of the gas in the lamp tube, after whichthe current drawn is such that the voltage output of the transformer israised and stabilized at about 110 volts A. C. With this type oftransformer it is not necessary to use a ballast and therefore the costand weight of such an element are eliminated. n

Gaseous discharge lighting equipment constructed in accordance with thisinvention makes use of a current converting device that is neither bulkynor heavy for its output. The device is inexpensive to make and isdependable in opera-l y to the opposite ends lof the two transformercoils and to the center tap of the primary coil. The use of atransformer permits layer winding and layer insulation,.which are theeasiest, without thought of bulk and weight.

According to the provisions of the patent statutes, I have explained theprinciple and operation of my invention and have illustrated anddescribed what I now consider to represent its best embodiment. However,I desire to have it understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallyillustrated and described.

I claim:

l. The combination with a gaseous discharge lamp provided with spacedfilaments, of a transformer having its secondary coil connected to saidfilaments, the primary coil of the transformer having a center tapadapted to be connected to a source of direct current that is to beconverted into alternating current, a pair of fixed electric -contactsconnected to the opposite ends of the primary coil, rotary contact meansfor connection to said source of direct current and adapted connected tosaid rotary contact means for driving said means to interrupt the flowof direct current to each half of said primary coil alternately wherebysaid secondary coil supplies alternating current to said lamp filaments,and means for stopping said rotary contact means in electrical contactwith one of said fixed contacts when the direct current to the primarycoil is shut oi to thereby assure self-starting of the armature whensaid current is turned on again.

2. The combination with a gaseous discharge lamp provided with spacedfilaments, of a transformer having its secondary coil connected to saidfilaments. the primary coil of thc transformer having a center tapadapted to be connected to a source of direct current that is to beconverted into alternating current, a pair of fixed aeiaiie electriccontacts connected to the opposite ends of the primary coil, rotarycontact means for connection to said source of direct current andadapted when rotating to make elcctricalcontact with each of said iixedcontacts alternately with a break between, a rotatable armatureoperatively connected to saidrotary Contact means for driving said meansto interrupt the flow of direct current to each half of said primarycoil alternately whereby said secondary coil supplies alternatingrcurrent to said lamp filaments, means for stopping said rotary contactmeans in electrical contact with one of said fixed contacts when thedirect current to the primary coil is turned oli, and means vforautomatically moving said stopping means out of operative position whensaid direct current is tuined o n again.

3. The combination with a gaseous discharge adapted to be successivelyattracted by periodic magnetic impulses of said transformer, meansconnecting-the rotary contact means to said armature for rotationthereby, a cam connected to said armature for rotation thereby,spring-biased means 'for engaging said cam when the direct current isturned oi whereby to stop said armature with one of its projectionsadjacent said transformer and with said rotary contact means inengagement with one of saidiixed contacts, and electromagnetic means forwithdrawing said spring-biased means from said cam when 'said primarycoil is energized.

5. The combination with a gaseous discharge lamp provided with spacedlaxnents, of a transformer having its secondary coil connected to saidfilaments, the primary coil of the transformer having a center tapadapted to be connected to a source of direct currect that is to beconverted into alternating current, a core for said coils having twoends facing each other, a pair of nxed electric contacts connected tothe opposite ends of the primary coil, rotary contact means forconnection to said source of direct current and lamp provided withspaced filaments, of a transformer having' its secondary coil connected-to said filaments, the primary coil of the trans- VUV nately with abreak between, a rotatable armature operatively connected to said rotarycontact means for driving said means to interrupt the now of directcurrent to each half of said coil altei-nately whereby said secondarycoil supplies al` teinating eurent to said lamp filaments, a stop membermounted for automatically stopping said armature in a predeterminedposition when the direct current is turned off, and electromagneticmeans for moving said stop member out of stopping position when saidprimary coil is energized.

e. The combination with a gaseous discharge lamp provided with spacedfilaments, of a transformer having its .secondary coil connected to saidnlaments, the primary coil ol' the transformer having acenter tapadapted to be connected to a source of direct current that isto beconverted into alternating current, a pair of fixed electric contactsconnected to the opposite ends oi the primary coil, rotary contact meansfor con'- nection to said source of direct current and adapted whenrotating to make electrical contact with each of said fixed contactsalternately with a break between whereby the circuit througn the primaryis periodically deeneigized and tlie current in said circuit liowsthrougn first one of said contacts and then the other to inducealternating current in said secondary, a rotatable armature having aplurality of radial projections adapted when rotating to make electricalcontact with each of said nxe'd contacts alternately with a breakbetween, and an armature rotatably mounted betweensaid core ends andadapted te be rotated by the periodical magnetic attraction of the core,said armature being operatively connected to said rotary contact meansfor driving the latter whereby to interrupt the iiow of direct 4 currentto each haii of said primary coil alternately and to alternatelyenergize and deener- .gize that coil.,

6. The combination withV a gaseous discharge lamp provided with spacedlaments, of atransformer having its secondary coil connected to of theprimary coil, rotary contact means adapted' to be electrically connectedto said source o dlrect current and adapted when rotating to makeelectrical contact with each of said fixed contacts alternately, and arotatable armature mounted I adjacent said core and having a pluralityof radial projections adapted to be successively attracted by periodicmagnetic impulses of the core, said armature being operatively connectedto said rotary contact means for rotation thereof whereby fto interruptthe :dow of direct current to each lamp provided with spaced filaments,of a transformer including concentric primary and secondary coils, thesecondary coil being connected to said filaments and the primary coil ofthe transformer having a center tap adapted to be connected to a sourceof direct` current that is to be converted into alternating current, amagnetic core common to both coils, a pair of nxed electric contactsconnected to the opposite ends of the primary coil, a rotatable shaft,an armature rigidly mounted on said shaft and adapted to be rotated byperiodic magnetic attraction of said core, and a commutator-like contactmember rigidly mounted on one end of said shaft and adapted to beconnected to said source of direct current, said contact member beingadapted when rotating to maire electrical contact alternately with eachof the xed contacts connected to the primary coil, whereby to interruptthe flow of direct current to each half of the primary coil alternatelyand to alternately energize and deenergize that coil.

8. The combination with a gaseous discharge lamp provided with spacedfilaments, of an auto matic switch electrically connecting the filamentsand adapted to open when said laments reach a predetermined temperature.to strike an arc between the iilaments, a transformer having itssecondary coil connected to said laments, the primary coil of thetransformer having a center tap adapted to be connected to a source ofdirect current that is to be converted 'into alternating current, a pairof xed electric contacts connected to the opposite ends of the primarycoil, rotary contact means for connection to said source of directcurrent and adapted when rotat ing to make electrical contact with eachof said nxed contacts alternately, and means for driving said rotarycontact means to interrupt the ilow of direct current to each half ofsaid primary coil alternately whereby said secondary coil suppliesalternating current to said lamp iilaments, said transformer having poorregulation characteristics to thereby cause the electrical resistance ofthe filaments before said switch opens to reduce the voltage of saidalternating current to a point at which it will not burn out thefilaments.

EDMUND G. LODGE.

